A United Nations University study into the environmental impact of PCs has found that extending a machine's operational life through reuse holds a much greater potential for energy saving than recycling.

According to the study, published on Monday, about 1.8 tonnes of raw material is required to manufacture the average desktop PC and monitor, about equal to that of a mid-sized car.

By far the best way to minimise impact on the environment from a PC is to extend its useful life, says Eric Williams, a researcher at the United Nations University in Tokyo and one of the report's co-authors.

Users should think carefully about whether they really need a new computer, if upgrading their existing computer could serve the same purpose, he says. Actions such as delaying replacement and upgrading the memory or storage space or, if the machine is replaced, donating the old computer so that it may continue to be used offer potential energy savings of between five and 20 times those gained by recycling.

This is because so much of the energy required to manufacture a PC is used to make high-tech components like semiconductors and those components are destroyed in the recycling process to collect a small amount of raw materials.

In an earlier study published in late 2002, Williams concluded that 3.8 pounds of fossil fuels and chemicals and 71 pounds of water are used to produce a single 0.07-ounce 32MB DRAM memory chip.